This invention relates to a gaseous discharge sputter coating apparatus having an improved target electrode structure which simplifies the construction and use of the apparatus and which is not subject to capacitive losses as are prior art structures.
It is necessary for many purposes to coat objects with one or more thin film of material. For example, most microelectronic components are produced by the application of thin films of conducting or semiconducting material onto a substrate surface. One of the primary types of apparatus used to apply such thin films relies on the sputtering phenomenon to provide the coating. That is, a target of the selected coating material is bombarded with high energy positive ions to effect removal of particles of the coated material from the target. The removed particles then deposit onto and adhere to substrate objects disposed in the line-of-sight of the bombarded target. The desired thin film is thus produced by the build-up on the substrate of the deposited particles.
The target sputtering and the deposition is most often obtained by forming a gaseous discharge between the target and an electrode such as the support for the substrate objects. Usually, the gaseous discharge is initiated and sustained by applying high frequency, e.g., radio frequency, electrical energy to the target or the other electrode structure. Samples of sputtering apparatuses of this type can be found in U.S. patent applications Ser. No. 625,733 filed Mar. 24, 1967, now abandoned; Ser. No. 662,637 filed Aug. 23, 1967, now abandoned; Ser. No. 668,107 filed Sept. 15, 1967, now U.S. Pat. No. 3,537,973; and Ser. No. 674,539 filed Oct. 11, 1967, now abandoned.
The target electrode structure for such an arrangement is usually in the form of a plate having a layer of the desired coating material on one face thereof. The plate is suspended within a chamber which encloses the substrate objects and which defines a controlled high vacuum environment for the gaseous discharge sputtering. It has been necessary in the past to include a grounding shield surrounding all surfaces of the plate, except for the face having the coating material, in order to confine the gaseous discharge to such face. If a grounding shield is not provided in prior art structures, sputtering of materials from surfaces of the electrode other than the surface having the desired material will occur. This will result in contamination of the coating applied to the substrate.
In order to be effective to prevent the formation of a gaseous discharge at surfaces of the target not made from the desired coating material, the grounding shield must be fairly closely spaced to the electrode. This results in capacitance between the electrode and the shielding, with resulting high power losses and, at times, arcing. Thus the intensity of the gaseous discharge and the desired sputtering is limited by such shields.
Other disadvantages are inherent in present systems in view of the necessity of locating the target electrode within a high vacuum chamber having a controlled environment to support the gaseous discharge. That is, relatively complicated electrical feed-through and cooling mechanisms must be provided through the wall of the vacuum chamber in order to connect the target electrode with electrical cooling medium sources exterior to such chamber. These complicated mechanisms are expensive and quite space consuming.